This report summarises the work conducted within the framework of two research projects a) Energy Matching b) Efficient solar rooftops. The scope of both the projects differs, however, there is a common technological aspect about evaluating solar air heating collectors for an energy efficient built environment. This is the central aspect of the report, where the techno-economic feasibility of two types of solar air heating collectors is evaluated. The first collector type considered is unglazed transpired solar collector, which is classically used for air heating in residential buildings across North America. The second collector type is a photovoltaic thermal air collector. The concept is to use existing PV settings by installing a heat recovery system to obtain an airflow behind the PV modules, and then use this heat for various purposes.
The project's scope restricts most of the boundary conditions regarding load, climate, and system configurations evaluated in this report. In total, four system configurations are identified which seem most suitable for the aforementioned solar collector technologies. The focus is on retrofitting these collectors in the existing energy system for a multi-family building cluster in Sweden. The system configurations evaluated includes:
a) Transpired collectors with exhaust air heat pump.
b) Transpired collectors with air source heat pump.
b) Photovoltaic thermal collectors for domestic hot water pre-heating.
d) Photovoltaic thermal collectors with air source heat pump for domestic hot water pre-heating.
The scope of analysis is limited to the energy, and economic performance of the whole system to evaluate the effect of the retrofit intervention of solar air heating collectors. The system is modelled using TRNSYS for three configurations and using Microsoft Excel for one specific configuration. The secondary objective is to evaluate the possibilities to improve solar collector performance on the system level, with a specific focus on the airflow control strategies for the collectors.
The results have shown that the integration of transpired collectors has a small but positive impact on the overall system performance for an exhaust air heat pump system. The control flow strategy developed effectively improves the system performance and thus annual savings. Despite this, the savings are not high enough to reach positive net present values during the collector's lifetime. The benefits are higher when the transpired collector is integrated with an ASHP, and the net present value is positive for this configuration. This configuration is implemented in one of the demo sites within the project.
The recovered heat from the PV collector can be more effectively used for direct domestic hot water pre-heating, rather than in series integration with heat pump. Comparing the savings from water pre-heating with the additional cost of installing heat recovery features in PV, the system will likely have a positive net present value. On the other hand, the effect with heat pump is quite small and thus results in lower savings.
This study can be used as a stepping stone towards identifying additional research opportunities for such systems.
2021.